Double-flow pump unit, and method for controlling same

ABSTRACT

A pump unit includes an electric motor and a pump with a duct. The pump is rotationally driven by the electric motor to provide a setpoint volumetric flow to the duct. A rotational speed controller is configured to, during operation of the pump, determine a setpoint rotational speed based on a fixed-point iteration of an initial rotational speed. The setpoint rotational speed is associated with a setpoint volumetric flow. The rotational speed controller is further configured to operate the pump at the setpoint rotational speed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase of PCT Appln. No. PCT/DE2020/100956 filed Nov. 6, 2020, which claims priority to DE 102019132770.9 filed Dec. 3, 2019, the entire disclosures of which are incorporated by reference herein.

TECHNICAL FIELD

The disclosure relates to a pump unit and to a method for controlling same, in particular for actuating and/or providing a supply to at least one component of a drive train of a motor vehicle by means of at least one setpoint volumetric flow, wherein a pump with at least one duct for the at least one setpoint volumetric flow is rotationally driven by an electric motor, and a rotational speed controller is provided for setting the at least one setpoint volumetric flow by means of rotational speed control of the pump.

BACKGROUND

A double-flow pump unit is described in the publication DE 10 2011 100 845 A1, wherein a first pump primarily cools components of a drive train and a second pump actuates a double clutch. Both pumps can be connected to a pressure accumulator by means of a hydraulic valve. Both pumps are controlled by means of a rotational speed control of an electric motor that drives them, wherein one of the pumps is separably connected to the electric motor by means of a clutch.

SUMMARY

It is desirable to provide a pump unit that is robust and controllable with a minimal computing effort and a method for controlling it.

The pump unit, according to one exemplary embodiment of the disclosure, in particular actuates and/or provides a supply to at least one component of a drive train of a motor vehicle. For example, a clutch, for example, a separating clutch between an internal combustion engine and an electric machine of a hybrid drive train, at least one friction clutch between an internal combustion engine and a transmission, a parking lock, one or both axially displaceable disks of a variator of a continuously variable belt transmission or the like can be actuated by means of the pump unit by means of a first pump flow that supplies a high-pressure duct. In addition, cooling of the clutch, the disk sets of the belt or the like and their lubrication can be provided; for example, by means of a second pump flow that supplies a low-pressure duct. By setting an appropriate speed for a given displacement volume and efficiency, the pump unit sets a volumetric flow at the appropriate duct—the high-pressure and/or low-pressure duct. The at least one single-flow or double-flow pump of the pump unit is rotationally driven by an electric motor. The electric motor is controlled to set a speed for providing the at least one volumetric flow by means of a control unit with a rotational speed controller that provides speed control of the electric motor and thus of the pump.

The setting of a specified volumetric flow such as the setpoint volumetric flow is based on the setpoint rotational speed depending on the displacement volume of the pump and its efficiency. In this case, an initial rotational speed is output by the rotational speed controller and the setpoint rotational speed is determined using a fixed-point iteration of this initial rotational speed during operation of the pump.

The pump unit can have a single-flow or a double-flow pump. In the case of a double-flow pump, the pump unit can have a first high-pressure duct for actuating a component and a second low-pressure duct for providing a supply to a component. According to one embodiment, the high-pressure duct and the low-pressure duct of a double-flow pump can be connected to one another by means of a pressure-limiting valve.

The proposed method is used to control the aforementioned pump unit with its specified characteristics. Here, with a system-related specified efficiency of the pump and a necessary setpoint volumetric flow to fulfill the task of the pump unit, an initial rotational speed of the pump is determined, for example estimated, and the electric motor is operated at this initial rotational speed. The setpoint rotational speed resulting from the displacement volume of the pump and its volumetric efficiency, which can be a function of a speed of the pump, a temperature of the pump fluid and the like, cannot be set directly for the setpoint volumetric flow required, i.e., to be set. To determine and set the setpoint rotational speed of the pump, a correction value is determined based on the set initial rotational speed and a predetermined number of iteration steps and the setpoint volumetric flow with a known displacement volume, with which the setpoint rotational speed is determined and set from the initial rotational speed. The setpoint rotational speed n_(set) results from equation (1)

n _(set) =Q _(Soll)/(V _(d)*η_(V))  (1)

where Q_(Soll) is the setpoint volumetric flow and V_(d) is displacement volume of the pump and the η_(V) is the volumetric efficiency. In this case, each iteration step results in reduced correction values, which improve the setpoint rotational speed as the number increases. The efficiency η_(V) can, for example, be read out and interpolated from loop tables stored in the control unit. Alternatively, the maximum efficiency known for the pump or an efficiency equal to one can be used as a good approximation.

Due to the rotational speed of the electric motor approaching the desired setpoint rotational speed with the number of iteration steps, with alternating over- and under-compensation of the correction values, for safety reasons, it may be advantageous to restrict the setpoint rotational speed to odd numbers, at least during the adjustment process during the fixed-point iteration, so that at the expense of an economical operation, a functionally reliable setpoint rotational speed is always determined and set. For most applications, for example, the fixed-point iteration can be limited to one with sufficient accuracy of the setpoint rotational speed, i.e., it is sufficient to determine only one iteration step with a single correction value and to correct the initial rotational speed with this correction value in order to obtain a sufficiently accurate setpoint rotational speed.

It can also be advantageous to apply a safety value to the setpoint rotational speed determined from the at least one iteration step. For example, a safety factor can be added to the setpoint rotational speed determined, or a safety sum can be added. The safety value can be constant or adapted to the operating situation; for example, operating age, temperature, setpoint rotational speed and/or the like.

In the case of a single-flow pump, it is sufficient if the setpoint rotational speed calculates the setpoint volumetric flow of the single duct. In the case of a double-flow pump with two ducts, in particular a high-pressure duct and a separate low-pressure duct, it is advantageous to determine the setpoint rotational speed for each one using the proposed fixed-point iteration and to operate the double-flow pump at the maximum setpoint rotational speed required for one of the two setpoint volumetric flows. Here, alternatively or additionally, the duct that is prioritized with regard to its function; for example, the high-pressure duct when a component is actuated, or the low-pressure duct in the case of a critical temperature or lubrication, can be preferred and its required setpoint rotational speed can be set.

In a double-flow pump with two ducts, namely a high-pressure duct and a low-pressure duct connected thereto by means of a hydraulic coupling, for example a pressure relief valve, a setpoint rotational speed can be determined for each duct after each iteration step. The maximum setpoint rotational speed required for one of the two setpoint volumetric flows can be determined from these two setpoint rotational speeds. The setpoint rotational speed for the current most important function can be prioritized. Subsequently or before the prioritization, the selected setpoint rotational speed can be corrected iteratively with a size of a volume exchange via the hydraulic coupling; for example, a volume loss via the pressure relief valve. This size of the volume exchange can be determined from the current efficiencies of the pump at the current speed of the low-pressure duct and the high-pressure duct.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is explained in more detail with reference to the exemplary embodiments shown in FIGS. 1 to 6 . In the figures:

FIG. 1 shows a schematic hydraulic plan for a single-flow pump unit,

FIG. 2 shows a method for operating the pump unit of FIG. 1 using a fixed-point iteration,

FIG. 3 shows a schematic hydraulic plan for a double-flow pump unit,

FIG. 4 shows a method for operating the pump unit of FIG. 3 using a fixed-point iteration,

FIG. 5 shows a schematic hydraulic plan for a double-flow pump unit with a hydraulic coupling of the ducts,

FIG. 6 shows a method for operating the pump unit of FIG. 5 using a fixed-point iteration.

DETAILED DESCRIPTION

FIG. 1 shows a schematically simplified representation of a pump unit 100 with a single-flow pump 105, which is rotationally driven by an electric motor 110, which sucks in hydraulic fluid from a sump 115 and feeds a setpoint volumetric flow Q_(Soll) into a duct 120; for example, for actuating a hydraulically operated clutch, parking lock or brake.

The setpoint volumetric flow Q_(Soll) is adjusted by a rotational speed controller 125 from a setpoint rotational speed n_(set) and a current actual rotational speed n_(act) of the pump 105.

The setpoint rotational speed n_(set) of the pump 105 of FIG. 1 is determined using a routine 130 shown in FIG. 2 . In block 135, the pump 105 is operated at an initial rotational speed n_(I), which is formed from the quotient of the desired setpoint volumetric flow Q_(Soll) and a displacement volume V_(d) of the pump 105. In a fixed-point iteration 140, when the pump 105 is running, in a run of one or more iteration steps, the current speed n_(act) of the pump 105 is assigned, for example by interpolation, from a table in block 145 with the characteristic diagram of speed-dependent efficiencies η_(V) and, if necessary, other variables such as a temperature of the hydraulic fluid and the like. The setpoint rotational speed n_(set) is then determined in block 150 from the quotient of the setpoint volumetric flow Q_(Soll) and the displacement volume V_(d) corrected with the efficiency η_(V). In order to carry out further iteration steps 155, if necessary, a branch is made to block 145. It has proven to be advantageous to carry out an odd number of iteration steps, in particular—as shown—only one iteration step. At the end of the fixed-point iteration 140, a safety value can be applied to the setpoint rotational speed n_(set) in block 160, as shown here, multiplied by a safety factor F greater than one.

FIG. 3 shows a schematically simplified representation of the pump unit 200 with a double-flow pump 205, which is rotationally driven by the electric motor 210, which sucks in hydraulic fluid from the sump 215 and feeds setpoint volumetric flows Q_(Cool), Q_(Sys) into two ducts, namely a low-pressure duct 220 and a high-pressure duct 221; for example, to cool or lubricate hydraulic components and to actuate a hydraulically actuated clutch, brake or parking lock.

The setpoint volumetric flows Q_(Cool), Q_(Sys) are adjusted by means of the rotational speed controller 225 from the setpoint rotational speed n_(set) and the current actual rotational speed n_(act) of the pump 205. The ratio of the setpoint volumetric flows Q_(Cool), Q_(Sys) to one another is specified here by the displacement volumes and the efficiency of the double-flow pump 205. Advantageously, the displacement volumes for the two ducts are similar.

Corresponding to the determination of the setpoint rotational speed n_(set) of pump unit 100 in FIG. 1 , the determination of the setpoint rotational speeds n_(set,LP), n_(set,HP) for setting the setpoint volumetric flows Q_(Cool), Q_(Sys) of the pump 205 of FIG. 3 is carried out separately from one another in the routine 230 shown in FIG. 4 .

In block 237, the pump 205 is operated at the initial rotational speed n_(I) rotational speed, which corresponds to the initial rotational speeds n_(I,LP), n_(I,HP) of blocks 235, 236, which is formed from the quotients of the desired setpoint volumetric flows Q_(Cool), Q_(Sys) and the displacement volume V_(d,LP), V_(d,HP) of the pump 205. In the fixed-point iteration 240, when the pump 205 is running, in a run of one or more iteration steps 255, the current speed n_(act) of the pump 205 is assigned, for example by interpolation, from the respective blocks 245, 246 with characteristic diagrams of the speed-dependent efficiencies η_(V,LP), η_(V,HP) and, if necessary, other variables such as the temperature of the hydraulic fluid and the like. The setpoint rotational speeds n_(set,LP), n_(set,HP) are then determined in blocks 250, 251 from the quotients of the setpoint volumetric flows Q_(Cool), Q_(Sys) and the displacement volume V_(d,HP), V_(d,LP) corrected with the efficiencies η_(V,LP), η_(V,HP).

For the robust and safe implementation of both the lubrication/cooling of components using the setpoint volumetric flow Q_(Cool) and the actuation of components using the setpoint volumetric flow Q_(Sys), the setpoint rotational speeds n_(set,LP), n_(set,HP) of blocks 250, 251 are compared with one another in block 265 and a setpoint rotational speed n_(set,Basis) is determined from the highest of the two setpoint rotational speeds n_(set,LP), n_(set,Hp). This setpoint rotational speed n_(set,Basis) is used to correct the pump 205.

To carry out further iteration steps 255, if necessary, a branch is made after block 265 to block 245. It has proven to be advantageous to carry out an odd number of iteration steps, in particular—as shown—only one iteration step.

At the end of the fixed-point iteration 240, a safety value can be applied to the setpoint rotational speed n_(set,Basis) in block 260, as shown here, multiplied by the safety factor F greater than one.

FIG. 5 shows the pump unit 300, which is similar to the pump unit 200 in FIG. 3 , in a schematically simplified representation with the double-flow pump 305, which is rotationally driven by the electric motor 310, which sucks in hydraulic fluid from the sump 315 and feeds the setpoint volumetric flows Q_(Cool), Q_(Sys) into the two ducts, namely the low-pressure duct 320 and the high-pressure duct 321; for example, to cool or lubricate hydraulic components and to actuate a hydraulically actuated clutch, brake or parking lock.

The setpoint volumetric flows Q_(Cool), Q_(Sys) are adjusted by means of the rotational speed controller 325 from the setpoint rotational speed n_(set) and the current actual rotational speed n_(act) of the pump 305. The ratio of the setpoint volumetric flows Q_(Cool), Q_(Sys) to one another is specified here by the displacement volumes and the efficiency of the double-flow pump 305. Advantageously, the displacement volumes for the two ducts are similar.

In contrast to the pump unit 200, a hydraulic coupling 370 is provided in the pump unit 300 between the high-pressure duct 321 and the low-pressure duct 320, so that the setpoint volumetric flows Q_(Cool) and Q_(Sys) are designed to be dependent on one another. The hydraulic coupling 370 is formed by a pressure-limiting valve 375, which is controlled by the system pressure of the high-pressure duct 321 and diverts an overpressure that occurs in the high-pressure duct 321 into the low-pressure duct 320, so that its setpoint volumetric flow Q_(Cool) can increase if required.

The routine 330 shown in FIG. 6 shows the control of the setpoint volumetric flows Q_(Cool), Q_(Sys) for the pump unit 300 of FIG. 5 based on the setpoint rotational speed n_(set,Basis). Here, the routine 330 corresponds to the routine 230 of FIG. 4 up to the determination of the setpoint rotational speed n_(set,Basis) in block 265. The setpoint rotational speed n_(set,Basis) determined in block 365 of the routine 330 or in another determination method is adapted to the influence of hydraulic coupling 370 in the additional fixed-point iteration 380. Reference is made to the procedure of routine 230 of FIG. 4 for determining the setpoint rotational speed n_(set,Basis).

The influence of the hydraulic coupling 370 is corrected in that the efficiencies η_(v,HP), η_(v,LP) are again determined from blocks 345, 346; for example, by means of interpolation, based on the previously determined setpoint rotational speed n_(set,Basis). In block 385, the corrected setpoint rotational speed n_(set,erw) is determined from the setpoint rotational speed n_(set,Basis), taking into account the determined efficiencies η_(v,HP), η_(v,LP). The corrected setpoint rotational speed n_(set,erw) results from the quotient of the numerator with the setpoint volumetric flow Q_(Sys) of the high-pressure duct 321 plus the product of the efficiency η_(v,LP) of the pump flow for the low-pressure duct 320, the displacement volume V_(d,LP) of the pump flow for the low-pressure duct 320 and the current setpoint rotational speed n_(set,Basis) and the denominator with the sum of the products of the efficiencies η_(v,HP), η_(v,LP) each multiplied by the displacement volumes V_(d,HP), V_(d,LP) of the pump ducts of the high-pressure duct 321 and the low-pressure duct 320.

If one or more iteration steps 390, in particular an odd number of iteration steps, are desired, a branch is made to the respective currently determined expanded setpoint rotational speed n_(set,erw) at the start of the fixed-point iteration.

At the end of the fixed-point iteration 380, a safety value can be applied to the corrected setpoint rotational speed n_(set,erw) in block 360, as shown here, multiplied by the safety factor F greater than one.

Based on the fixed-point iteration 380 shown, multi-dimensional tables that depict the hydraulic influence of the hydraulic coupling 370 and their complex algorithmic consideration can be dispensed with.

LIST OF REFERENCE SYMBOLS

-   100 Pump unit -   105 Pump -   110 Electric motor -   115 Sump -   120 Duct -   125 Rotational speed controller -   130 Routine -   135 Block -   140 Fixed-point iteration -   145 Block -   150 Block -   155 Iteration step -   160 Block -   200 Pump unit -   205 Pump -   210 Electric motor -   215 Sump -   220 Low-pressure duct -   221 High-pressure duct -   225 Rotational speed controller -   230 Routine -   235 Block -   236 Block -   237 Block -   240 Fixed-point iteration -   245 Block -   246 Block -   250 Block -   251 Block -   255 Iteration step -   260 Block -   265 Block -   300 Pump unit -   305 Pump -   310 Electric motor -   315 Sump -   320 Low-pressure duct -   321 High-pressure duct -   325 Rotational speed controller -   330 Routine -   345 Block -   346 Block -   360 Block -   365 Block -   370 Hydraulic coupling -   375 Pressure-limiting valve -   380 Fixed-point iteration -   385 Block -   390 Iteration step -   F Safety factor -   n_(act) Current actual rotational speed -   n_(I) Initial rotational speed -   n,^(IHP) Initial rotational speed -   n_(I,LP) Initial rotational speed -   n_(set,HP) Setpoint rotational speed -   n_(set,LP) Setpoint rotational speed -   n_(set) Setpoint rotational speed -   n_(set,Basis) Setpoint rotational speed -   n_(set,erw) Setpoint rotational speed -   Q_(Cool) Setpoint volumetric flow -   Q_(Soll) Setpoint volumetric flow -   Q_(Sys) Setpoint volumetric flow -   V_(d) Displacement volume -   V_(d,HP) Displacement volume -   V_(d,LP) Displacement volume -   η_(V) Efficiency -   η_(V,HP) Efficiency -   η_(V,LP) Efficiency 

1. A pump unit, comprising: an electric motor; a pump having a duct and being rotationally driven by the electric motor to provide a setpoint volumetric flow to the duct, and a rotational speed controller configured to: during operation of the pump, determine a setpoint rotational speed of the pump based on a fixed-point iteration of an initial rotational speed of the pump, wherein the setpoint rotational speed is associated with a setpoint volumetric flow; and operate the pump at the setpoint rotational speed.
 2. The pump unit according to claim 1, wherein the pump includes a second duct, the pump being rotationally driven by the electric motor to provide a second setpoint volumetric flow to the second duct.
 3. The pump unit according to claim 2, wherein the duct and the second duct are hydraulically coupled to one another via a pressure-limiting valve.
 4. The pump unit according to claim 2, wherein the duct is a high-pressure duct configured to actuate a component, and the second duct is a low-pressure duct configured to provide a fluid supply to the component, and wherein the component is a clutch, a parking lock, or a disk set of a variator of a continuously variable belt transmission.
 5. A method for controlling a pump unit, comprising: determining an initial rotational speed of the pump based on an efficiency of the pump and a required setpoint volumetric flow, wherein the efficiency is a maximum efficiency for the pump or is equal to one; determining a setpoint rotational speed based on a specified number of iteration steps of the initial rotational speed and a correction value from the efficiency of the pump, wherein the correction value is determined based on the initial speed and the setpoint volumetric flow, wherein the setpoint rotational speed is associated with a setpoint volumetric flow; and operating the pump at the setpoint rotational speed.
 6. The method according to claim 5, wherein the specified number of iteration steps is odd.
 7. The method according to claim 5, further comprising applying a safety value to the setpoint rotational speed.
 8. The method according to claim 5, wherein the pump unit includes two ducts separate from each other, the method further comprising: determining the initial rotational speed of the pump for each duct based on the efficiency of the pump for respective duct and the required setpoint volumetric flow for each duct; determining the setpoint rotational speed of the pump for each duct based on the specified number of iteration steps of the initial rotational speed for the respective duct and the correction value of the efficiency for the respective duct; and operating the pump at a maximum of the determined setpoint rotational speeds.
 9. The method according to claim 5, wherein the pump includes two ducts connected to each other via a hydraulic coupling, the method further comprising: determining the initial rotational speed of the pump for each duct based on the efficiency of the pump for respective duct and the required setpoint volumetric flow for each duct; determining the setpoint rotational speed of the pump for each duct based on the specified number of iteration steps of the initial rotational speed for the respective duct and the correction value of the efficiency for the respective duct; determining a corrected setpoint rotational seed based on a maximum of the determined setpoint rotational speeds, and a volume exchange via the hydraulic coupling; and operating the pump at the corrected setpoint rotational speed.
 10. The method according to claim 9, wherein a size of the volume exchange is determined from the efficiencies of the pump for the ducts at the maximum of the determined setpoint rotational speeds.
 11. The pump unit according to claim 2, wherein the rotational speed controller is further configured to determine a second setpoint rotational speed based on a fixed-point iteration of a second initial rotational speed of the pump, the second setpoint rotational speed being associated with the second setpoint volumetric flow.
 12. The pump unit according to claim 11, wherein the rotational speed controller is further configured to operate the pump at a maximum of the setpoint rotational speed and the second setpoint rotational speed.
 13. The pump unit according to claim 11, wherein the rotational speed controller is further configured to selectively operate the pump at one of the setpoint rotational speed or the second setpoint rotational speed.
 14. The pump unit according to claim 11, wherein the rotational speed controller is further configured to determine the second initial rotational speed based on a desired setpoint volumetric flow through the second duct and a displacement volume of the pump through the second duct.
 15. The pump unit according to claim 14, wherein the rotational speed controller is further configured to determine the second setpoint rotational speed further based on an efficiency of the pump operating via the second duct.
 16. The pump unit according to claim 11, wherein the rotational speed controller is further configured to determine the initial rotational speed based on a desired setpoint volumetric flow through the duct and a displacement volume of the pump through the duct.
 17. The pump unit according to claim 16, wherein the rotational speed controller is further configured to determine the setpoint rotational speed further based on an efficiency of the pump operating via the duct.
 18. The pump unit according to claim 1, wherein the rotational speed controller is further configured to determine the initial rotational speed based on a desired setpoint volumetric flow and a displacement volume of the pump.
 19. The pump unit according to claim 18, wherein the rotational speed controller is further configured to determine the setpoint rotational speed further based on an efficiency of the pump.
 20. The pump unit according to claim 3, wherein the rotational speed controller is further configured to: determine a volume exchange via the hydraulic coupling based on an efficiency, at the maximum setpoint rotational speed, of the pump for each duct; determine a corrected setpoint rotational speed based on the volume exchange and the maximum setpoint rotational speed; and operate the pump at the corrected setpoint rotational speed. 